The present invention relates to curved rolls or bars useful in the control of flexible sheet or web materials, and more particularly to curved rolls or bars, the radius of curvature of which is adjustable. The present invention also relates to straight rolls or bars which may be adjustably curved in opposite directions in a single plane.
Longitudinally curved rolls or bars of a type whose degree of curvature is adjustable have found wide use for the lateral spreading and expansion of sheet materials such as cloth, paper, foil, plastic film, webs of tire cord and the like, both to control the width of the material and to remove wrinkles. Such rolls or bars are also used for correcting bow distortions of the weft threads of woven goods or the courses of knit goods. Although in many applications curved rolls or bars having a fixed degree of curvature or bow are satisfactory, it is often necessary or desirable to provide means for changing the curvature of the roll or bar in order to obtain better control of the processing under varying conditions.
In known rolls, it has proven to be advantageous to incorporate a tension and a compression member within a centrally positioned axle of the roll. In U.S. Pat. No. 3,838,480 a solid axle is split, and a threaded screw-like adjusting means applies tension to one split portion of the axle and compression to another portion of the axle which lies on the opposite side of a neutral bending axis of the axle. The equally applied tension and compression causes a change in the curvature of the axle. Rolls having one piece, split axles have a number of shortcomings. First, the bending force is not evenly distributed across the axle. Also, if either the tension or compression members break, the entire axle must be rebuilt, and the cost of the construction is high.
In other known adjustable deflection rolls, such as the roll of U.S. Pat. No. 3,500,524, a compression member and a tension member are snugly fit within a hollow, circular, straight cylindrical axle. The two members extend lengthwise within the axle, and they meet on a neutral axis of transverse bending of the axle. The two members are longitudinally slidable relative to one another and to the axle. When the curvature of the roll is adjusted, the member being compressed lies on the convex side and the member which is in tension lies toward the concave side. To adjust the tension and compression members, two adjusting screws for each member -- one located at each end of a member -- are rotated by an amount appropriate to provide the necessary compression and tension. This roll, however, is not a bowed roll. Rather it is a straight roll which deflects, and in operation the roll will attempt to return to a straight position. Such rolls, also only adjust in one direction, and they cannot reverse the direction.
Adjustable deflection rolls of the type described in U.S. Pat. No. 3,500,524 also have a number of shortcomings. First of all, screws must be adjusted on both ends of the roll, and therefore, clearance must be left on both sides of the rolls. Such a need for clearance prevents the rolls from being used in certain tight environments, and in fact, most web processing machines have only a single "tending" side from which adjustments are made. Secondly, the increased length imposes difficulties and limitations where such rolls are required to be mounted between the frames of an existing machine. Thirdly, the two screws must be rotated by an equally opposite amount, and the accuracy of such adjustment will never be perfect. Finally, the roll can only be adjusted in one direction from a straight or curved condition, this limits maximum adjustment to only 50% of what could be achieved with the same elements with adjusting force reversal.
It is therefore a principal object of the present invention to provide an adjustable-curvature roll or bar utilizing separate tension and compression members inserted in a hollow, cylindrical axle, the curvature of which can be accurately and reliably adjusted in both directions from the neutral position.
It is a further object of the present invention to provide an adjustable-curvature roll having separate tension and compression members, both of which are actuated by the turning of a single adjusting means located on one end of the roll.